Mutations in Dystonin (DST), which encodes cytoskeletal linker proteins, cause hereditary sensory and autonomic neuropathy 6 (HSAN-VI) in humans and the dystonia musculorum (dt) phenotype in mice; however, the neuronal circuit underlying the HSAN-VI and dt phenotype is unresolved. dt mice exhibit dystonic movements accompanied by the simultaneous contraction of agonist and antagonist muscles and postnatal lethality. Here, we identified the sensory-motor circuit as a major causative neural circuit using a gene trap system that enables neural circuit-selective inactivation and restoration of Dst by Cre-mediated recombination. Sensory neuron-selective Dst deletion led to motor impairment, degeneration of proprioceptive sensory neurons, and disruption of the sensory-motor circuit. Restoration of Dst expression in sensory neurons using Cre driver mice or a single postnatal injection of Cre-expressing adeno-associated virus ameliorated sensory degeneration and improved abnormal movements. These findings demonstrate that the sensory-motor circuit is involved in the movement disorders in dt mice and that the sensory circuit is a therapeutic target for HSAN-VI.

BACKGROUND: Pain perception, far from being a pathological mechanism, is a crucial protective stimulus to prevent additional injuries. Any disturbance in this complex system poses significant risks to individuals, affecting their quality of life and even their survival.
OBJECTIVE: This review aims to explore congenital insensitivity to pain, an extremely rare genetic disorder with an autosomal recessive pattern that results in the inability to perceive pain. We will focus on the well-known subtype, congenital insensitivity to pain with anhidrosis (CIPA). Our research seeks to update existing knowledge through a comprehensive literature review.
METHODS: The review employs a systematic literature review, analyzing various sources and scientific documents, primarily emphasizing CIPA. The review follows the PROSPERO protocol, registered under CRD42023394489. The literature search was performed on the Scopus, PubMed, and Cinahl databases.
RESULTS: Our review reveals secondary complications associated with CIPA, such as recurrent bone fractures, temperature insensitivity, self-mutilation, and, occasionally, intellectual disabilities. The limited available information underscores the need for expanding our knowledge.
CONCLUSIONS: In summary, CIPA, particularly, presents a significant medical challenge with adverse impacts on quality of life. Early diagnosis, education for families and healthcare professionals, and appropriate nursing care are essential for effective management. This review highlights the necessity of further research and awareness to enhance support for those affected.

Hereditary sensory and autonomic neuropathy type 1 is an autosomal dominant neuropathy caused by the SPTLC1 or SPTLC2 variants. These variants modify the preferred substrate of serine palmitoyl transferase, responsible for the first step of de novo sphingolipids synthesis, leading to accumulation of cytotoxic deoxysphingolipids. Diagnosis of HSAN1 is based on clinical symptoms, mainly progressive loss of distal sensory keep, and genetic analysis. Aim: Identifying new SPTLC1 or SPTLC2 \"gain-of-function\" variants raises the question as to their pathogenicity. This work focused on characterizing six new SPTLC1 variants using in silico prediction tools, new meta-scores, 3D modeling, and functional testing to establish their pathogenicity. Methods: Variants from six patients with HSAN1 were studied. In silico, CADD and REVEL scores and the 3D modeling software MITZLI were used to characterize the pathogenic effect of the variants. Functional tests based on plasma sphingolipids quantification (total deoxysphinganine, ceramides, and dihydroceramides) were performed by tandem mass spectrometry. Results: In silico predictors did not provide very contrasting results when functional tests discriminated the different variants according to their impact on deoxysphinganine level or canonical sphingolipids synthesis. Two SPTLC1 variants were newly described as pathogenic: SPTLC1 NM_006415.4:c.998A>G and NM_006415.4:c.1015G>A. Discussion: The combination of the different tools provides arguments to establish the pathogenicity of these new variants. When available, functional testing remains the best option to establish the in vivo impact of a variant. Moreover, the comprehension of metabolic dysregulation offers opportunities to develop new therapeutic strategies for these genetic disorders.

Motor neuron diseases and peripheral neuropathies are heterogeneous groups of neurodegenerative disorders that manifest with distinct symptoms due to progressive dysfunction or loss of specific neuronal subpopulations during different stages of development. A few monogenic, neurodegenerative diseases associated with primary metabolic disruptions of sphingolipid biosynthesis have been recently discovered. Sphingolipids are a subclass of lipids that form critical building blocks of all cellular and subcellular organelle membranes including the membrane components of the nervous system cells. They are especially abundant within the lipid portion of myelin. In this review, we will focus on our current understanding of disease phenotypes in three monogenic, neuromuscular diseases associated with pathogenic variants in components of serine palmitoyltransferase, the first step in sphingolipid biosynthesis. These include hereditary sensory and autonomic neuropathy type 1 (HSAN1), a sensory predominant peripheral neuropathy, and two neurodegenerative disorders: juvenile amyotrophic lateral sclerosis affecting the upper and lower motor neurons with sparing of sensory neurons, and a complicated form of hereditary spastic paraplegia with selective involvement of the upper motor neurons and more broad CNS neurodegeneration. We will also review our current understanding of disease pathomechanisms, therapeutic approaches, and the unanswered questions to explore in future studies.

Hereditary sensory autonomic neuropathy type VIII (HSAN-VIII) is a rare genetic disease that occurs due to mutations in the PRDM12 gene. Here, we describe a novel homozygous mutation c.826_840dupTGCAACCGCCGCTTC (p.Cys276_Phe280dup) on exon 5 in the PRDM12 gene identified by WES and confirmed using Sanger sequencing method.

BACKGROUND: PRDM12 polyalanine tract expansions cause two different disorders: midfacial toddler excoriation syndrome (MiTES; itch with normal pain sensation associated with 18 homozygous alanines (18A); and congenital insensitivity to pain (CIP) with normal itch associated with 19 homozygous alanines (19A). Knowledge of the phenotype, genotype and disease mechanism of MiTES is incomplete. Why 18A vs. 19A PRDM12 can cause almost opposite phenotypes is unknown; no other polyalanine or polyglutamine tract expansion disease causes two such disparate phenotypes.
OBJECTIVE: To assess the genotype and phenotype of nine new, nine atypical and six previously reported patients diagnosed with MiTES.
METHODS: Using cell lines with homozygous PR domain zinc finger protein 12 (PRDM12) containing 12 alanines (12A; normal), 18A (MiTES) and 19A (CIP), we examined PRDM12 aggregation and subcellular localization by image-separation confocal microscopy and subcellular fractionation Western blotting.
RESULTS: MiTES presents in the first year of life; in all cases the condition regresses over the first decade, leaving scarring. The MiTES phenotype is highly distinctive. Features overlapping with PRDM12 CIP are rarely found. The genotype-phenotype study of the PRDM12 polyalanine tract shows that having 7-15 alanines is normal; 16-18 alanines is associated with MiTES; 19 alanines leads to CIP; and no clinically atypical cases of MiTES had a polyalanine tract expansion. PRDM12 aggregation and subcellular localization differed significantly between 18A and normal 12A cell lines and between 18A and 19A cell lines. MiTES is a new protein-aggregation disease.
CONCLUSIONS: We provide diagnostic criteria for MiTES and improved longitudinal data. MiTES and CIP are distinct phenotypes, despite their genotypes varying by a single alanine in the PRDM12 polyalanine tract. We found clear distinctions between the cellular phenotypes of normal, MiTES and CIP cells. We hypothesize that the developmental environment of the trigeminal ganglion is unique and critically sensitive to pre- and postnatal levels of PRDM12.
Midfacial toddler excoriation syndrome (MiTES) causes facial itching and scratching in babies during their first year of life. MiTES tends to improve over the time period of approximately 10 years, but it can leave scars. Congenital insensitivity to pain (CIP) is a condition where a person cannot feel pain and is present from birth. This study looked at two conditions: MiTES and CIP. We specifically investigated changes in a gene called PRDM12, focusing on a part of the gene called the polyalanine tract – a sequence of many alanines (alanine is a type of amino acid). We discovered that the normal range for this sequence is between 7 and 15 alanines. If there are 16 to 18 alanines, it is associated with MiTES and causes the PRDM12 protein to clump together inside the cell. However, if there are 19 alanines, it leads to CIP, and the PRDM12 protein clumps together and moves to the cytoplasm, where it should not be. We found new evidence to suggest that MiTES is a disease where proteins clump together. Overall, our study findings show that despite there only being a small change in the same gene, MiTES and CIP are very different conditions.

BACKGROUND: Congenital insensitivity to pain with anhidrosis (CIPA) is an extremely rare autosomal recessive disorder caused by loss-of-function mutations of the NTRK1 gene, affecting the autonomic and sensory nervous system. Clinical manifestation is varied and includes recurrent fever, pain insensitivity, anhidrosis, self-mutilating behavior, and intellectual disability.
METHODS: Clinical and genetic features were assessed in two males and one female with genetically confirmed CIPA using exome or genome sequencing.
RESULTS: CIPA symptoms including recurrent fever, pain insensitivity, and anhidrosis manifested at the age of 1 year (age range: 0.3-8 years). Two patients exhibited self-mutilation tendencies, intellectual disability, and developmental delay. Four NTRK1 (NM_002529.3) mutations, c.851-33T>A (p.?), c.2020G>T (p.Asp674Tyr), c.2303C>T (p.Pro768Leu), and c.574-156_850+1113del (exons 5-7 del) were identified. Two patients exhibited early onset and severe phenotype, being homozygous for c.851-33T>A (p.?) mutations and compound heterozygous for c.851-33T>A (p.?) and c.2020G>T (p.Asp674Tyr) mutation of NTRK1. The third patient with compound heterozygous mutations of c.2303C>T (p.Pro768Leu) and c.574-156_850+1113del (exons 5-7 del) displayed a late onset and milder clinical manifestation.
CONCLUSIONS: All three patients exhibited variable phenotypes and disease severity. This research enriches our understanding of clinical and genetic aspects of CIPA, highlighting variable phenotypes and disease severity.

BACKGROUND: Hereditary sensory and autonomic neuropathy type IV (HSAN IV) may be misdiagnosed because of low awareness among clinical professionals and overlap with other subtypes of congenital insensitivity to pain (CIP).
METHODS: The patient was a 1-year-and-5-months-old boy whose main symptoms were delayed psychomotor development and recurrent fever. Whole-exome sequencing (WES) revealed a compound heterozygous mutation (c. 1927C > T, c. 851-33T > A) in the NTRK1 gene of the child. Pathological analysis showed decreased autonomic small nerve fibers, sparse hair follicles, and atrophy of the sweat glands. Sweat glands lack innervating nerve fibers. Brain magnetic resonance imaging (MRI) of the patient showed delayed myelination in the brain, slightly enlarged bilateral lateral ventricles, and patchy abnormal signals in the brain.
METHODS: hereditary sensory and autonomic neuropathy type IV (HSAN IV).
METHODS: Inform parents about the illness and take good care of the child.
RESULTS: The children had less self-harming behavior and no painless fractures during follow-up at 2 years.
CONCLUSIONS: This report describes the pathological and imaging features and clinical manifestations of a child with HSAN IV in early life to provide a reference for the early diagnosis of the disease. Early diagnosis can help avoid self-mutilation and painless injury and reduce wound infection.

Hereditary sensory and autonomic neuropathy type 4 (HSAN4), also known as congenital insensitivity to pain with anhidrosis (CIPA), is a rare genetic disorder caused by NTRK1 gene mutations, affecting nerve growth factor signaling. This study investigates the central nervous system\'s (CNS) involvement and its relation to pain insensitivity in HSAN4. We present a 15-year-old girl with HSAN4, displaying clinical signs suggestive of CNS impact, including spasticity and a positive Babinski\'s sign. Using Technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (Tc-99m ECD SPECT) imaging, we discovered perfusion deficits in key brain regions, notably the cerebellum, thalamus, and postcentral gyrus. These regions process pain signals, providing insights into HSAN4\'s pain insensitivity. This study represents the first visualization of CNS perfusion abnormality in an HSAN4 patient. It highlights the intricate relationship between the peripheral and central nervous systems in HSAN4. The complexity of HSAN4 diagnosis, involving potential unidentified genes, underscores the need for continued research to refine diagnostic approaches and develop comprehensive treatments.

Congenital insensitivity to pain with anhidrosis (CIPA) is an extremely rare disease characterized by insensitivity to pain, anhidrosis, and intellectual disability. CIPA is caused by a genetic mutation in the neurotrophic tyrosine receptor kinase 1 (NTRK1) gene on chromosome 1. The anhidrosis leads to cutaneous changes such as skin dryness, lichenification, and impetiginization. Moreover, patients with CIPA may experience repeated trauma and recalcitrant eczema due to excessive scratching of wounds on their skin, because they do not feel any pain. Severe whole-body eczema in a patient with CIPA may be overlooked, leading these patients to be frequently diagnosed with atopic dermatitis and common eczema. Indeed, in patients with treatment-resistant or atypically distributed eczema and underlying anhidrosis, CIPA should be considered as a potential causative disease. Increased awareness of CIPA among dermatologists is necessary to ensure that patients receive an appropriate diagnosis. Herein, we report a rare case of generalized xerotic eczema in a patient with CIPA.